Ghosts in the fuel pump circuit?

[mlatten]

...And I thought I was out of the SHO game...

Last week my cousin buys a 95 ATX from a friend of mine. The car had issues passing inspection last year due to really high CO's. About three months ago the car decides its done starting. So when my cousin buys it he asks me to have a look at it. The fuel pump was not priming, but the IRCM was new from Ford. So after a week of stewing, I cut a hole in the back seat and replace the pump.

Car starts right up.

Wonderful, I think, the deed is done. As I'm driving it to my cousin's though, the pump cuts out! It wasn't getting power at the jack on the top of it. Wrestle the car off the road, open up the back seat, inspect the pump and put it back together, the thing comes back to life!

Drive it back at my house where it sits for 3 days. I go to start it again today, fuel pump is dead! So after 2 hours of pulling fuses, carpet and whatever else, I crank the car over and as I'm letting off the key I hear the pump again. Now it's working!

So after a thorough analysis, here's what I have: Fuel pump and IRCM are new. DIS is replaced with a known good one from another automatic. Cut off switch in trunk is fine. Connections at all of these locations are cherry. I followed the pump wire every which way and there are no signs of corrosion, pinched, or broken wires ANYWHERE!!!

How can something like this just be intermittent? It must be ghosts, right? BTW, whenever the pump won't prime, there is no power to the jack itself.

Thank god I cut the hole and didn't drop the tank!

Sorry for the long post, but I'm so frustrated right now!
Matt

 

[93rev2sev]

I'll refer you to another post...very recent one at that...

http://www.shoforum.com/showthread.php?t=86294

 

[mlatten]

I ripped out the driver seat and took another look at the two harnesses that are there, but there's no sign at all of melting, corroding, or pinching. Furthermore, when I get the thing running, I can beat it all day long and it won't cut out . . . in fact, earlier it cut out while idling!

Very frustrating, but thank you for that link.

Matt

 

[SolidState]

this is definitely a wiring issue.

I missed the fuel pump plug the first time. You need to LIFT the main wiring harness to get at it.

did you check the voltage at the fuel sender plug? did you bypass the inertia switch in the trunk? You need to jumper the fuel pump to make it run at idle speed for these tests.

to check if the ground is good, tap the black fuel pump ground wire at the sender and ground to the body of the car. Use the bolt for the rear seat back as a temporary ground to test.

FYI, the wiring at the pump is as follows:

PINK/BLACK: 12v Power to FP
BLACK: Ground to FP
YELLOW/WHITE: 12v to Fuel Gage
ORANGE/YELLOW: Ground to Fuel Gage.

 

[SHOZ123]

Here is something to try. When it is running good check for voltage drop along the different connectors in the circuit. This should point to the problem.

Say the voltage is 13.5 at the input side of the inertia switch and 12.5 at the output would suggest the switch is bad.

 

[SolidState]

yeah, that is actually one of the pinpoint tests on the Ford CD I have. Voltage must be nearly identical on both sides of the switch.

 

[89 black SHO mtx]

just curious if the problem was found? I have the same issue with 90 and haven't found anything "wrong". Also does anyone know of a post in here for the wiring diagram of the fuel pump system?